Insulated electrical equipment

ABSTRACT

An annular guard ( 20 ) for mounting on a high voltage insulator extends laterally thereof for a sufficient distance so as to prevent small wildlife such as squirrels from forming a short circuit between the opposing ends of the insulator at high voltage and earth potential respectively. The guard ( 20 ) is formed in two planar parts ( 24, 26 ) that are pivoted together ( 28 ) so that they can be relatively rotated between an open condition for mounting onto a live insulator and a closed condition for being secured thereto. Overlapping regions of the two parts are secured together ( 30, 32, 34, 36, 38 ) in the closed condition.

This invention relates to an insulating article for protectingelectrical equipment and to such equipment having the article mountedthereon.

Electrical equipment, such as power transmission lines, insulators,surge arrestors, switchgear and transformers, operating at voltages inexcess of 1 kV and particularly in excess of 10 kV (such voltageshereinafter being referred to as ‘high voltage’), often have partsthereof or parts associated therewith that are not insulated from thesurrounding air. Thus, an exposed portion of such equipment can be athigh voltage and be longitudinally separated from another portion at lowvoltage, for example at earth potential. The exposed high voltageportion may be physically supported by an insulator, for example when anoverhead power line is mounted on an insulator that spaces it from asupporting tower that is itself at earth potential, or for example whena high voltage cable is terminated at a bushing or switchgear whosemetal housing is at earth potential. In such instances outdoors, thelarger wildlife such as squirrels and birds with large wingspans may bebig enough to form a direct bridge, ie. an electrical short circuit,between the high voltage equipment and earth potential, with serious,usually fatal, consequences for themselves and often with seriousconsequences for the electrical equipment and the supply of electricalpower—usually at least a fuse is actuated or a circuit breaker triggeredsuch that the power supply is interrupted.

One solution to this problem is to insulate the exposed parts of thehigh voltage equipment, at least in regions where a short circuit toearth is more likely to occur, for example unintentionally by wildlife,and products such as RAYSULATE insulation tapes and pre-shapedcomponents are available from Raychem for this purpose. Such componentsinclude heat-recoverable polymeric sheds, which may be mounted onporcelain sheds of existing insulators so as to increase the creepagelength thereof, or otherwise so as to improve electrical performance.Although such products may incidentally make it more difficult forwildlife to bridge the electrical terminals of an insulator, theirdesign is not optimised for this purpose and their method ofinstallation in some circumstances may not be particularly convenient.

Another solution is to mount an insulating guard on the apparatus so asphysically to increase the distance between the two portions at suchsignificantly different, ie. harmful, electrical potentials such that itis impossible, or at least more unlikely, that the wildlife will be ableto form a direct bridge therebetween. A typical insulator for outdooruse may be made of porcelain or polymeric material and is usuallyprovided with a plurality of rain sheds or skirts, that extendcircumferentially around a central cylindrical core of the insulator andthat are spaced apart along its length. A protective guard, referred toas a squirrel shield device, for preventing short-circuiting of such aninsulator by wildlife is disclosed in WO 95/10844, the guard comprisingtwo semi-circular discs that are brought together from each side of theinsulator between two adjacent sheds. The semi-circular discs partiallyoverlap and are interlocked, for example by means of projections on aface of one disc that engage apertures in the other disc. The diameterof the guard is typically about three times that of the sheds, and whenin place provides an effective obstacle to wildlife prostratingthemselves along the length of the shedded insulator from earth to highvoltage. However, a guard of this configuration is not very convenientto position on the insulator, which may be difficult to access, as beingmounted on top of a pole of about 4 m height for example. It isnecessary to support the two halves separately, bring them together inoverlapping relationship, and then to operate the interlockingmechanism. This usually cannot be done from a distance, from groundlevel for example, and the power supply to the electrical equipment, tothe power line supported on the insulator for example, may have to beinterrupted in order properly to fit the guard.

A generally disc-shaped polymeric insulating article for protectingelectrical equipment such as a high voltage insulator is disclosed in WO96/16416. This article is also in two parts, with a first part beingsubstantially C-shaped to fit around the insulator core, and a secondpart comprising an insert that slidably engages the first part so as tosecure the article in place.

It has been known for many years to mount additional barriers, sometimesreferred to as booster sheds or creepage extenders, on to porcelain orpolymeric insulators in order to improve their electrical performance.Such barriers are of generally circular or conical configuration and areto be mounted on the core of the insulator or on existinglaterally-extending sheds thereof. It is advantageous for retrofittingsuch barriers on to insulators that are already connected into anelectrical supply or distribution system, for them to be of wraparoundconfiguration so as to avoid the need for any dismounting of theinsulator. Thus, these barriers are annular and have a radial slit thatis generally closed after positioning around the insulator.GB-A-1542845, WO 92/08237, and EP-A-0328365 exemplify articles of thiskind. GB-A-1542845 discloses an annular discharge barrier of integralconstruction that is wrapped around the insulator and closed by having aseries of pegs press fitted tightly into holes at overlapping edges. WO92/08237 discloses an annular barrier that may be integral or that maybe formed of a plurality of components connected together withdiscontinuities therebetween. Closure of this barrier may be by a rodextending through loops or by the peg and hole system of GB-A-1542845.The barrier of WO 92/08237, which although initially may be formed as aflat sheet, has to adopt a frusto-conical configuration when it isclosed around an insulator by overlapping its free edges. EP-A-0328365discloses a wraparound creepage extender whose free ends need not beconnected together, but which may be secured by fasteners. Difficultiesmay be experienced with products having these features in securing themon to the underlying insulator, especially if that is still connected toa power source.

It is one object of the present invention to provide an article that canmore conveniently be mounted on electrical equipment so as electricallyto protect the equipment, and thus associated electrical components,from being short-circuited, for example due to the presence of wildlife.

Thus, in accordance with one aspect of the present invention, there isprovided a substantially planar electrically insulating article forprotecting electrical equipment that is of generally elongateconfiguration and that has two longitudinally spaced-apart portionsthat, in operation, are at significantly different electricalpotentials, the article comprising:

(a) two substantially planar parts that are linked to each other at apivot point such that relative rotation of the two parts about the pivotpoint causes the parts to move between an open condition and a closedcondition of the article, wherein, in the open condition, the articlecan be applied to the elongate electrical equipment, and wherein, in theclosed condition, the article encircles the equipment so as to extendgenerally transversely thereof; and

(b) closure means arranged to secure the two parts of the articletogether when in the closed condition so as to retain the articlesecurely mounted on the equipment.

The direct distance between the two portions at significantly differentelectrical potentials is the shortest distance between those portionsthat could be bridged by wildlife such as squirrels or large birds, andis typically about twelve to fourteen inches minimum.

The insulating article of the present invention is thus provided as arelatively rigid component that can be applied in an open condition tothe electrical equipment effectively as a single article but whose partscan be rotated relative to one another about the pivot point to bring itto the closed condition so as conveniently to close it around and tosecure it to the equipment. Furthermore, and unlike the barrier shedsdiscussed above, the pivotal movement of the two parts ensures that thearticle of the invention retains its planar configuration as it movesfrom its open condition to its closed condition. Thus, for any givenlateral, usually radial, dimension in the open configuration, an articlein accordance with the present invention will allow its lateraldimension in the closed configuration to be maximised. This is animportant feature for the application of wildlife protection, but is notso relevant for known articles that are designed purely for improvingthe continuous electrical performance of the insulator, for example bytheir ability, having a generally conical configuration, to shed wateraway from the insulator.

When the article is applied to the electrical equipment, it mayinitially be disposed loosely therearound and be supported thereby. Inthe closed condition, it may abut, and may be secured to, the encircledequipment. It is envisaged, however, that even in the closed condition,in which the article can no longer simply be displaced off theequipment, the article may be a loose fit, for example as by beingrotatable, on the equipment.

Preferably the two parts of the article overlap each other in the closedcondition of the article, and the closure means extends through anaperture in at least one part in the overlapping region.

The closure means may comprise means extending through the or eachaperture arranged to tie the two parts of the article together.Insulating thread or tape may be used, but a tie-wrap polymeric memberthat is self-locking is preferred.

In another embodiment, the two parts of the article may be closed bymeans of a wedge that drives the parts together around the insulator.Advantageously, the wedge is substantially co-planar with the article,and may interengage therewith by means of a ratchet mechanism.

In other embodiments, the closure means may comprise a pin, or bolt orprojection, and may be secured to one of the parts and arranged toco-operate with the other part in a manner so as to secure the twotogether. For example, the pin may have an enlarged head at its free endand may co-operate with a keyhole-shaped slot in the other part. In thisembodiment, the pinhead enters the slot at its larger-apertured end, andslides therealong so as to be retained therein and simultaneously tosecure the two parts of the article together. In another embodiment, thefree end and shank of the pin may pass into an aperture of the othermember that is ratcheted, for example by having a suitably shaped innerperiphery, so as to grip the pin and to resist its withdrawal from theaperture. The inner periphery may be star-shaped for example or may beslitted. It is also envisaged, however, that the aperture may be ofslightly smaller size than the pin to effect its securement.

In a further embodiment, one or both of the parts may have a channel, orgroove or slot, in its outer periphery, by means of which the parts maybe tied together. For example, a tie-wrap or other tying member mayextend around channels in the two parts so as to pull them securelyaround the electrical equipment. Alternatively, the tying member may beretained in or on one of the parts, for example as by passing through anaperture therein, and may engage a channel in the other part.

In a still further embodiment, a pin of the closure means may beretained in or on one of the parts, its free end extending through anaperture in the other part. The pin may be threaded, and may thuscomprise a bolt, and a co-operatively-threaded nut may be employed tosecure it in place.

It is also envisaged that the closure means may be integrally formedwith the article, such as, for example, the parts thereof snap-fittingtogether.

Usually, the electrical equipment on which the article of the inventionis mounted is of generally circular cross-section, and its diameter maybe within a predetermined range depending, for example, on its voltagerating. It is advantageous therefore if a single insulating article canbe provided that has a range-taking ability so that it can be used withdifferently-sized pieces of electrical equipment. Range-taking, whilstmaintaining the ability to achieve secure retention of the article onthe equipment, can be enhanced if the central aperture fully defined bythe two parts of the article is delineated by one, or preferably a pair,of substantially U- or V-shaped surfaces; for example one such surfacebeing provided by each of the parts of the article. The extent ofinterengagement of the two parts, such as the extent to which the partsare able to close around the electrical equipment, will then varydepending on the diameter, or other transverse dimension, of theelectrical equipment. Preferably at least one of the parts, andadvantageously each of them, is provided with at least one apertureadjacent its inner periphery such that the article is arranged, inoperation, to engage the electrical equipment resiliently, thus furtherenhancing the range-taking ability.

For ease and cheapness of manufacture, the two parts of the article areadvantageously of the same size and shape.

Usually, the article will be of circular shape, and preferably planar,in the form of a disc. The pivot point will usually be adjacent theouter periphery, and the closure of the two parts will be locateddiametrically opposed thereto.

Although the article of the invention, in keeping with the equipment onwhich it is mounted, is generally of substantially circular shape, itwill be appreciated that the object of avoiding formation of a directbridge over a relatively short path length between two parts ofelectrical equipment at significantly different electrical potentials,may be achieved by a laterally-extending insulating article of differentshape, and reference to ‘disc-shape’ is to be interpreted accordingly.

The two parts that form the protective surface area of the article maybe substantially identical, or they may be complementarily—shaped withrespect to each other, but this need not necessarily be so.

In accordance with another aspect of the present invention there isprovided a substantially planar electrically insulating article forprotecting electrical equipment that is of generally elongateconfiguration and that has two longitudinally spaced apart portionsthat, in operation, are at significantly different electricalpotentials, the article comprising:

(a) at least three substantially planar parts that are sequentiallylinked together at pivot points such that relative rotation of the partsabout the pivot points causes the parts to move between an opencondition and a closed condition of the article, wherein, in the opencondition, the article can be applied to the elongate electricalequipment, and wherein, in the closed condition, the article encirclesthe equipment and so as to extend generally transversely thereof; and

(b) closure means arranged to secure together the two extreme ones ofthe plurality of parts of the article when in the closed condition so asto retain the article securely mounted on the equipment.

Each part and the closure means of the article of this other aspect ofthe invention may be as hereinbefore and hereinafter described.

Advantageously the insulating article of the invention, and preferablyboth parts thereof, is formed from polymeric material such aspolyethylene, EPDM or silicone, which preferably is also substantiallyelectrically non-tracking as defined in ASTM D2303. The use of such highelectrical quality materials allows articles mounted on insulators ofadjacent pieces of electrical equipment, for example uninsulatedoverhead power lines, to come into close proximity, for example overlap,with each other, or even to touch, without any significant deteriorationin the electrical performance.

In yet another aspect of the present invention, there is providedelectrical equipment, for example an electrical insulator or power cabletermination, having mounted thereon at least one substantially planarelectrically insulating article in accordance with the invention ashereinbefore described.

In cases where the equipment is fitted with laterally-extending rainsheds, the insulating article of the present invention will usuallyextend laterally a significantly further distance from the core of theequipment. For example, the insulating guard article may be generallycircular and have a diameter twice or even three, or more, times that ofthe rain shed associated with the equipment, and four, five or moretimes that of a cylindrical core of the equipment—when the equipmentcomprises a shedded insulator for example. Furthermore, the rain shed orsheds may be of frusto-conical configuration angled generally downwards,with the insulating article of the invention extending substantially atright angles to a longitudinal, for example vertical, axis of theequipment.

The equipment may be orientated substantially vertically, substantiallyhorizontally, or at any other angle.

Advantageously, one, and preferably both parts of the article of theinvention are apertured such that any equipment or apparatus that ismounted beyond, for example above or behind, the article is visibletherethrough.

The electrical equipment may comprise, for example, a stand aloneinsulator, or the insulator may function as an insulating bushing ofswitchgear or a transformer. The insulating function may also becombined with another function, such as by the equipment comprising afuse, a circuit breaker or a surge arrestor.

One particular advantage of the article of the invention is that it canbe installed relatively easily, and can be done so ‘live’, that is tosay without having to switch off the power to the associated electricalequipment, an overhead power line for example. In this way, much timeand money can be saved by avoiding the need for carrying out earthingand other safety procedures, and for supplying customers temporarilywith electrical power by another route.

Several embodiments of insulating wildlife guard and electricalequipment protecting article, and electrical equipment protected by thearticle, in accordance with the present invention, will now bedescribed, by way of example, with reference to the accompanyingdrawings in which:

FIG. 1 is a schematic elevation of a high voltage insulator fitted withthe insulating article;

FIG. 2 is a plan view of one embodiment of the article of the invention;

FIG. 3 is a plan view of another embodiment of the article of theinvention;

FIG. 4 shows another embodiment of a closure means;

FIG. 5 shows a portion of a further embodiment of insulating guard; and

FIG. 6 shows a plan view of a yet further embodiment of the article.

Referring to FIG. 1, an elongate high voltage insulator 2 for outdooruse is made of porcelain and comprises a generally cylindrical core 4 ofapproximate diameter 12 cms (4½ inches) and four longitudinally spacedapart rain sheds 6 of approximate diameter 20 cms (eight inches)integral therewith. The insulator 2 is mounted vertically on an earthedmetal base 8, and supports an uninsulated high voltage conductor 10 bybeing bolted thereto at 12. The shortest direct distance between theearthed plinth 8 and the conductor 10 at high voltage, is approximately50 cms (20 inches), a distance that can be bridged by certain forms ofwildlife. To safeguard such wildlife and also the continuity of supplyof electrical power along the conductor 10, a generally circulardisc-shaped polymeric insulating guard 14 of diameter twenty four inchesis mounted on the insulator 2. The guard 14 is fixed to the core 4 ofthe insulator 2 about halfway along its length. With the guard 14 inposition on the insulator 2, the direct distance between earth and highvoltage is significantly increased.

One embodiment of the insulating guard is shown at 20 in FIG. 2, andcomprises two planar arcuate parts 24, 26. The parts 24, 26 are shownpartially open. The parts are mounted on a swivel hinge 28 where theyoverlap. The closure arrangement comprises a pin 30 loosely retained ina slot 32 of the part 24 at a location diametrically opposed to thehinge 28, and a keyhole-shaped slot 34 of the part 26 also locateddiametrically opposite the hinge 28. Upon swivelling the parts 24, 26 tobring article 20 to a closed condition, the enlarged head 36 of the pin30 is located adjacent the larger-apertured end 38 of the slot 34, isurged therethrough, and is subsequently urged along the shank, or narrowportion, of the slot 34 as the two parts 24, 26 are brought intoengagement with the electrical equipment (not shown) extendingtherethrough. In a more preferred embodiment, the elongate slot 32 isdispensed with, the pin 30 merely passing as an easy fit through acorrespondingly-shaped aperture in the guard part 24, with range-takingof the assembled guard being accommodated substantially solely by thekeyhole-shaped slot 34 of the part 26.

The pin 30 of the embodiment of FIG. 2 may be replaced by a bolt, whichmay be captured in the part 24, that may tighten the parts 24 and 26 ofthe guard together by means of a co-operating nut.

The central region 40 of each part 24, 26 is cut away to define aU-shape such that different sizes, eg. diameters, of equipment can belocated within the same article by varying the extent of the closing ofthe parts. An elongate aperture 42 is provided in the parts 24, 26adjacent each limb of the central region. The apertures 42, inassociation with the resilience of the polymeric material from which thearticle 20 is made, allow for a certain amount of compressibility andthus enhance the range-taking capability of the insulating guard.

Each article part 24, 26 is punctured by circular apertures 44 lover themajor area of its surface to allow visibility through the otherwiseopaque article.

The embodiment 50 of insulating guard shown in FIG. 3 differs from theguard 20 of FIG. 2 in its closure mechanism. The two parts 52, 54 of theguard 50 are substantially identical, and at their periphery remote fromthe pivot point 56 have a circumferential extension 58, 60 that providesan aperture 62 therethrough and a channel 64. A polymeric tie-wrap 66 isretained in the aperture 62 of the part 52. When the two parts 52, 54are closed around the centrally-located piece of electrical equipment(not shown), the still-open tie-wrap 66 is looped through the channel 64of the other part 54, and secured so as to pull the central region ofthe guard 50 tightly into engagement with the equipment.

FIG. 4 shows a modification of the closure arrangement, for use with aninsulating guard having an aperture in at least one of the parts in theregion where they overlap in the closed condition.

The closure arrangement comprises a pin 70 (shown in side view) havingan enlarged head and a cylindrical shank, and a retaining washer 72(shown in end view). The washer 72 has an irregular, ie. non-smooth,inner periphery, for example being of star shape, that receives theshank of the pin 70 as a push-fit therein, but subsequently resistswithdrawal of the pin. The pin 70 is passed through overlappingapertures of the two parts of the insulating guard when the guard is infirm abutment with the electrical equipment, and the washer 72 isfitted, thereby to hold the two parts firmly in position.

FIG. 5 shows schematically a portion of an insulating guard thatcomprises a plurality of parts, only three of which 90, 92, 94 beingshown, that together completely encircle the electrical equipment. Eachpart is hinged at 96 to each of its neighbours, and on closing aroundthe equipment a closure arrangement of suitable form secures all theparts on the equipment.

The insulating guard 100 shown in FIG. 6 has two substantially planarand substantially semi-circular major portions 102, 104 interconnectedby a hinge pin 106 located approximately midway along a radius of theguard. The portions 102, 104 have a slot 108 therebetween in the regionbeyond the pin 106 and the adjacent periphery. Opposing edges of thecomponents along the slots 108 are of toothed configuration, and areengageable by a mating wedge 110.

The guard 100 is shown in the closed position, with the wedge 110inserted in ratchet engagement with the slot 108 so as to bring the twoguard portions 102, 104 into contact with a centrally-located insulatorcore 112. The central V-shaped cut-outs 114, 116 in the portions 102,104 respectively allow for range-taking such that the guard 100 can fiton to insulators 112 of a variety of diameters. The portions 102, 104are apertured at 118, for visibility through the article, and also toallow the article to be gripped by a tool to allow it to be positionedon the insulator 112. The locking wedge 110 also has an aperture 120 toallow it to be gripped for insertion into the slot 108.

Although in the embodiments disclosed, the insulating guards usuallycontact the supporting insulator when in the closed condition, this neednot be so. In some instances it may be sufficient for the guard to beretained loosely around the core, and to be supported by resting on alateral shed of the insulator.

It is envisaged that any combination of parts and closure arrangementsdisclosed herein that will produce a functional insulator guard, may beselected.

What is claimed is:
 1. A substantially planar electrically insulatingarticle for protecting elongate electrical equipment, the electricalequipment having two longitudinally spaced-apart portions that, inoperation, are at different electrical potentials, the articlecomprising: two substantially planar parts connected to each other at apivot point such that relative rotation of the two parts about the pivotpoint causes the parts to move between an open condition and a closedcondition of the article, wherein, in the open condition, the articlecan be applied to the electrical equipment, and wherein, in the closedcondition, the article encircles the electrical equipment so as to beretained thereon and to extend generally transversely thereof; and a pinwith an enlarged head secured to one of the parts and a keyhole-shapedaperture in the other part, wherein the enlarged head of the pin isinsertable into a wider portion of the keyhole aperture and is slideabletherealong into a narrower portion and securable therein so as to securethe two parts of the article together in the closed condition around theelectrical equipment.
 2. A substantially planar electrically insulatingarticle for protecting elongate electrical equipment, the electricalequipment having two longitudinally spaced-apart portions that, inoperation, are at different electrical potentials, the articlecomprising: two substantially planar parts connected to each other at apivot point such that relative rotation of the two parts about the pivotpoint causes the parts to move between an open condition and a closedcondition of the article, wherein, in the open condition, the articlecan be applied to the electrical equipment, and wherein, in the closedcondition, the article encircles the electrical equipment so as to beretained thereon and to extend generally transversely thereof, each ofthe parts having an inner periphery and an outer periphery; a retainingchannel in the outer periphery of a first one of the parts configured toreceive and retain a tie wrap so as to enable the first part to be tiedto the other part; and a second retaining channel in the outer peripheryof the other part, offset from the retaining channel of the first one ofthe parts in the closed condition, configured to receive and retain thetie wrap so as to enable the two parts to be tied together or anaperture in the outer periphery of the other part, offset from theretaining channel of the first one of the parts in the closed condition,configured to receive and retain the tie wrap so as to enable the twoparts to be tied together.
 3. An article according to claim 1 whereinthe inner periphery of each part of the article is of substantially U-or V-shape so as, in operation, to abut the electrical equipmentextending therethrough and to accommodate such equipment having a rangeof cross-sectional dimensions.
 4. A substantially planar electricallyinsulating article for protecting elongate electrical equipment, theelectrical equipment having two longitudinally spaced-apart portions,that in operation, are at different electrical potentials, the articlecomprising: two substantially planar parts connected to each other at apivot point such that relative rotation of the two parts about the pivotpoint causes the parts to move between an open condition and a closedcondition of the article, wherein, in the open condition, the articlecan be applied to the electrical equipment, and wherein, in the closedcondition, the article encircles the electrical equipment so as to heretained thereon and to extend generally transversely thereof, each ofthe parts having an inner periphery and an outer periphery; closuremeans arranged to secure the two parts of the article together when inthe closed condition; and wherein at least one of the two parts isprovided with at least one elongate aperture adjacent its innerperiphery, the at least one elongate aperture being positioned toincrease the articles range-taking, such that the article is arranged,in operation, resiliently to engage the electrical equipment extendingtherethrough.
 5. An article according to claim 4, wherein the two partsthereof are of substantially the same shape and size.
 6. An articleaccording to claim 4, being of substantially disc shape in its closedcondition.
 7. An article according to claim 4, wherein the pivot pointis located adjacent the outer periphery of the article and the closuremeans is located at a corresponding point opposed thereto adjacent theouter periphery.
 8. A substantially planar electrically insulatingarticle for protecting electrical equipment that is of generallyelongate configuration and that has two longitudinally spaced apartportions that, in operation, are at significantly different electricalpotentials, the article comprising: (a) at least three substantiallyplanar parts that are sequentially linked together at pivot points suchthat relative rotation of the parts about the pivot points causes theparts to move between an open condition and a closed condition of thearticle, wherein, in the open condition, the article can be applied tothe elongate electrical equipment, and wherein, in the closed condition,the article encircles the equipment and extend generally transverselythereof; and (b) closure means arranged to secure together the twoextreme ones of the plurality of parts of the article when in the closedcondition so as to retain the article securely mounted on the equipment.9. An article according to claim 8, made from a material comprisingelectrically insulating and substantially electrically non-trackingpolymeric material.
 10. An article according to claim 8, wherein thepivot point and the closure means are arranged to be located on oppositesides of the elongate electrical equipment.
 11. An article according toclaim 8, wherein the pivot point and the closure means are arranged tobe located on the same side of the elongate electrical equipment, andwherein the closure means comprises a wedge that interacts with the twoplanar parts of the article.
 12. An article according to claim 11,wherein the wedge and the planar parts are substantially co-planar andinterengage by means of a ratchet mechanism.
 13. An article according toclaim 8, wherein at least one of the parts thereof is apertured, wherebyany equipment mounted therebeyond is visible therethrough. 14.Electrical equipment that is of generally elongate configuration andthat has two longitudinally spaced-apart portions that, in operation,are at significantly different electrical potentials, and that hasmounted thereon intermediate said spaced-apart portions at least onearticle according to claim
 8. 15. Electrical equipment according toclaim 14, having a generally cylindrical core extending through the oreach article, with the or each article extending transversely to theaxis of the core.
 16. Electrical equipment according to claim 14comprising an elongate core and at least one rain shed extendinglaterally therefrom, wherein said at least one article extends laterallyfrom the core by an amount greater than the lateral extension of therain shed.
 17. Electrical equipment according to claim 16, wherein saidat least one article is mounted on said at least one rain shed. 18.Electrical equipment according to claim 14, comprising an electricalinsulator, a bushing of switchgear or a transformer, or a surgearrester.
 19. A substantially planar electrically insulating article forprotecting elongate electrical equipment, the electrical equipmenthaving two longitudinally spaced-apart portions that, in operation, areat different electrical potentials, the article comprising: twosubstantially planar parts connected to each other at a pivot point suchthat relative rotation of the two parts about the pivot point causes theparts to move between an open condition and a closed condition of thearticle, wherein, in the open condition, the article can be applied tothe electrical equipment, and wherein, in the closed condition, thearticle encircles the electrical equipment so as to be retained thereonand to extend generally transversely thereof; a wedge receiving cutoutin at least one of the parts, the pivot point and the wedge receivingcutout being located on the same side of the elongate electricalequipment when the article encircles the electrical equipment; and awedge configured to be positioned in the wedge receiving cutout tosecure the two parts of the article together when in the closedposition.
 20. An article according to claim 19 wherein the wedge and theplanar parts are substantially co-planar and interengage at a ratchetmechanism defined by an edge of the wedge receiving cutout.